2,702 research outputs found
Constraints on the operation of a DI diesel engine in partially-premixed combustion mode
Partially-premixed Charge Compression Ignition (PCCI) combustion is defined by increased levels of premixed charge whilst retaining control over combustion through injection timing. An experimental investigation has been carried out on a current generation DI diesel engine, equipped with High Pressure Common Rail (HPCR) fuel injection equipment and an external Exhaust Gas Recirculation (EGR) system. The aims of the investigation were to determine the constraints imposed on operating a PCCI combustion strategy with the aim of simultaneously reducing engine-out net soot and NOx emissions.
The work was carried out at fully-warm steady-state conditions at engine speeds of 1500 rpm and 1800 rpm, predominantly using a single injection strategy. With a single injection the Start of Injection (SOI), fuel rail pressure, and rate of EGR have been examined with a view to realising PCCI combustion. Timing ranges of -20Âș to +3ÂșATDC, rail pressures of 500-1200 bar, and EGR rates of 0-60% have been investigated. The responses looked at have been engine-out soot, NOx, HC, and CO emissions, fuel consumption, and combustion noise. It is shown that variation of the parameters has allowed PCCI combustion to be achieved in a restricted operating region, offering improvement in the NOx-soot trade-off. This region is limited on the available test engine by oxygen availability due to the specifications of the turbocharger and EGR systems. Engine speeds up to 2000 rpm (at 2.5 bar BMEP), and loads of 4.4 bar gross IMEP (at 1500 rpm) have been found to be the limits, beyond which soot and CO emissions rise excessively.
It is shown that enhancing the mixing time and intensity are both desirable in achieving PCCI combustion. The net soot reduction mechanism exploited with PCCI combustion strategies is reducing soot formation to outweigh the reduction in oxidation. Enhancing the mixing intensity by increasing injection pressure is highly effective at reducing soot output, but at the expense of brake specific fuel consumption. Increasing the mixing time can also be effective in reducing soot output, but careful parameter selection is required to avoid excessive soot output. Retarded or highly advanced injection timings are shown to reduce net soot output, but both have associated trade-offs and penalties. Retarding combustion is effective at lowering soot and NOx emissions with low associated noise, but a fuel economy penalty is paid. Advanced combustion phasing can result in large peak rates of increase of pressure, which have been shown to correlate well with combustion noise. Overall soot reductions of up to 97% were achieved, but with associated penalties. One of the most acceptable reductions of ~90% came at the cost of a 6% increase in fuel consumption, highlighting that improvements in emissions are achievable with PCCI strategies with acceptable trade-offs
Constraints on the operation of a DI diesel engine in partially-premixed combustion mode
Partially-premixed Charge Compression Ignition (PCCI) combustion is defined by increased levels of premixed charge whilst retaining control over combustion through injection timing. An experimental investigation has been carried out on a current generation DI diesel engine, equipped with High Pressure Common Rail (HPCR) fuel injection equipment and an external Exhaust Gas Recirculation (EGR) system. The aims of the investigation were to determine the constraints imposed on operating a PCCI combustion strategy with the aim of simultaneously reducing engine-out net soot and NOx emissions.
The work was carried out at fully-warm steady-state conditions at engine speeds of 1500 rpm and 1800 rpm, predominantly using a single injection strategy. With a single injection the Start of Injection (SOI), fuel rail pressure, and rate of EGR have been examined with a view to realising PCCI combustion. Timing ranges of -20Âș to +3ÂșATDC, rail pressures of 500-1200 bar, and EGR rates of 0-60% have been investigated. The responses looked at have been engine-out soot, NOx, HC, and CO emissions, fuel consumption, and combustion noise. It is shown that variation of the parameters has allowed PCCI combustion to be achieved in a restricted operating region, offering improvement in the NOx-soot trade-off. This region is limited on the available test engine by oxygen availability due to the specifications of the turbocharger and EGR systems. Engine speeds up to 2000 rpm (at 2.5 bar BMEP), and loads of 4.4 bar gross IMEP (at 1500 rpm) have been found to be the limits, beyond which soot and CO emissions rise excessively.
It is shown that enhancing the mixing time and intensity are both desirable in achieving PCCI combustion. The net soot reduction mechanism exploited with PCCI combustion strategies is reducing soot formation to outweigh the reduction in oxidation. Enhancing the mixing intensity by increasing injection pressure is highly effective at reducing soot output, but at the expense of brake specific fuel consumption. Increasing the mixing time can also be effective in reducing soot output, but careful parameter selection is required to avoid excessive soot output. Retarded or highly advanced injection timings are shown to reduce net soot output, but both have associated trade-offs and penalties. Retarding combustion is effective at lowering soot and NOx emissions with low associated noise, but a fuel economy penalty is paid. Advanced combustion phasing can result in large peak rates of increase of pressure, which have been shown to correlate well with combustion noise. Overall soot reductions of up to 97% were achieved, but with associated penalties. One of the most acceptable reductions of ~90% came at the cost of a 6% increase in fuel consumption, highlighting that improvements in emissions are achievable with PCCI strategies with acceptable trade-offs
Biases From Spectral Leakage in Remote Sensing of Near-Surface Currents
Postprint version of published articleRemotely measuring subsurface water currents from imagery of the wave field has become a much-used technique. We study the biases and errors in such measurements due to spectral leakage and suggest mitigating procedures. Deviations between peak values in the 3-D wave spectrum and the known dispersion relation in quiescent water are extracted and interpreted as current-induced Doppler shifts, from which the subsurface current is inferred. The use of discrete Fourier transforms (DFTs), however, introduces spectral leakage between nearby frequency bins. Analyzing synthetically generated wave data adhering to realistic input spectra, we show that although no current is, in fact, present, spurious currents can be âmeasured,â which can amount to a significant fraction of the phase speed at the spectral peak. We analyze the effects of data tapering, method of Doppler shift extraction, limited wavenumber and frequency resolution, peakedness and angular width of the input spectrum, and average misalignment between waves and Doppler shift velocity (DSV) direction. The narrower the input wave spectrum in frequency and/or direction, the greater the biases become. The use of a window function reduces the severity in nearly all cases, yet mitigates the effects of limited resolution more effectively in space than in time. When a current is present, the absolute biases remain essentially unchanged, when waves and currents are roughly aligned; whereas in the case of a cross current, biases remain significant even for tapered data.acceptedVersio
On the measurement of the dispersion relation by a radar and the implication on the current retrieval
The work analyses the error in current retrievals from images of marine
radars. The study is based on simulations of waves interacting with a shear
current. The measured dispersion is related to the underlying
wavenumber-dependent effective current. The highest tested radar antenna (H=45
m) with vertical polarization performed the best. For that case the root mean
square error was at most 0.05 m/s above the one for the simulated wave field
without imaging mechanism. The observation time of 20 minutes was compared to
shorter windows. Depending on the needed accuracy, the time may be reduced to
five minutes, associated with an loss of accuracy below 12%. The study shows
the error of the current reconstruction depends on the shape of the profile and
varies considerably from realization to realizatio
Induction of Group IVC Phospholipase A2 in Allergic Asthma: Transcriptional Regulation by TNF-α in Bronchoepithelial Cells
Airway inflammation in allergen-induced asthma is associated with eicosanoid release. These bioactive lipids exhibit anti- and pro-inflammatory activities with relevance to pulmonary pathophysiology. We hypothesized that sensitization/challenge using an extract from the ubiquitous fungus, Aspergillus fumigatus (Af), in a mouse model of allergic asthma would result in altered phospholipase gene expression, thus modulating the downstream eicosanoid pathway. We observed the most significant induction in the group IVC phospholipase A2 (cPLA2Îł or PLA2G4C). Our results infer that Af extract can induce cPLA2Îł levels directly in eosinophils while induction in lung epithelial cells is most likely a consequence of TNF-α secretion by Af-activated macrophages. The mechanism of TNF-α-dependent induction of cPLA2Îł gene expression was elucidated through a combination of promoter deletions, ChIP and overexpression studies in human bronchoepithelial cells, leading to the identification of functionally relevant CRE, NF-ÎșB and E-box promoter elements. ChIP analysis demonstrated that RNA polymerase II, c-Jun/ATF-2, p65/p65 and USF1/USF2 complexes are recruited to the cPLA2Îł enhancer/promoter in response to TNF-α with overexpression and dominant negative studies implying a strong level of cooperation and interplay between these factors. Overall, our data link cytokine-mediated alterations in cPLA2Îł gene expression with allergic asthma and outline a complex regulatory mechanism
Investigating the Putative RecA-Like Recombinase Gene
Our Biochemistry: Molecular Genetics class has partnered with the Immunology class to investigate the expression of JacoRen57âs gene 50.
The bacteriophage JacoRen57 â found in Sioux Center, Iowa (accession: MK279840). JacoRen57âs genome has sequenced by Pittsburg SEA-PHAGES Institute and fully annotated by Northwestern College students in 2018. A region between gene 49 and 50 caught our attention as there is a large gap between these genes. Almail et al., investigated if this is a transcription regulatory region for genes 49 and/or 50 (2021). This work demonstrated the region has a regulatory function in the direction of gene 50. Based on comparison genomics, gene 50 is a putative RecA-like recombinase (Almail et al., 2019). This protein has several functions including guiding the recombination of DNA within a gene. RecA-like recombinase allows the virus to evolve into new variants which can improve infection and replication.âŻThis is crucial for creating diversity in the genome and DNA repair mechanisms (Galletto and Kowalczykowski, 2007).
To continue examination of gene 50 expression, we are working towards developing antibodies for this protein. To do this, the first step is to create an expression construct (Figure 1), express the protein in bacteria, purify the protein, and then use the purified protein to inoculate mice. This poster describes the construction of the expression vector. This work will provide valuable insight into the expression of gene 50, the RecA-like recombinase
Localization of supersymmetric field theories on non-compact hyperbolic three-manifolds
We study supersymmetric gauge theories with an R-symmetry, defined on
non-compact, hyperbolic, Riemannian three-manifolds, focusing on the case of a
supersymmetry-preserving quotient of Euclidean AdS. We compute the exact
partition function in these theories, using the method of localization, thus
reducing the problem to the computation of one-loop determinants around a
supersymmetric locus. We evaluate the one-loop determinants employing three
different techniques: an index theorem, the method of pairing of eigenvalues,
and the heat kernel method. Along the way, we discuss aspects of supersymmetry
in manifolds with a conformal boundary, including supersymmetric actions and
boundary conditions.Comment: v3:79p, minor clarifications and references adde
Basal epithelial stem cells cross an alarmin checkpoint for postviral lung disease
Epithelial cells are charged with protection at barrier sites, but whether this normally beneficial response might sometimes become dysfunctional still needs definition. Here, we recognized a pattern of imbalance marked by basal epithelial cell growth and differentiation that replaced normal airspaces in a mouse model of progressive postviral lung disease due to the Sendai virus. Single-cell and lineage-tracing technologies identified a distinct subset of basal epithelial stem cells (basal ESCs) that extended into gas-exchange tissue to form long-term bronchiolar-alveolar remodeling regions. Moreover, this cell subset was selectively expanded by crossing a cell-growth and survival checkpoint linked to the nuclear-localized alarmin IL-33 that was independent of IL-33 receptor signaling and instead connected to autocrine chromatin accessibility. This mechanism creates an activated stem-progenitor cell lineage with potential for physiological or pathological function. Thus, conditional loss of Il33 gene function in basal epithelial cells disrupted the homeostasis of the epithelial barrier at skin and gut sites but also markedly attenuated postviral disease in the lung based on the downregulation of remodeling and inflammation. Thus, we define a basal ESC strategy to deploy innate immune machinery that appears to overshoot the primordial goal of self-defense. Our findings reveal new targets to stratify and correct chronic and often deadly postviral disease
Jet energy measurement with the ATLAS detector in proton-proton collisions at root s=7 TeV
The jet energy scale and its systematic uncertainty are determined for jets measured with the ATLAS detector at the LHC in proton-proton collision data at a centre-of-mass energy of âs = 7TeV corresponding to an integrated luminosity of 38 pb-1. Jets are reconstructed with the anti-kt algorithm with distance parameters R=0. 4 or R=0. 6. Jet energy and angle corrections are determined from Monte Carlo simulations to calibrate jets with transverse momenta pTâ„20 GeV and pseudorapidities {pipe}η{pipe}<4. 5. The jet energy systematic uncertainty is estimated using the single isolated hadron response measured in situ and in test-beams, exploiting the transverse momentum balance between central and forward jets in events with dijet topologies and studying systematic variations in Monte Carlo simulations. The jet energy uncertainty is less than 2. 5 % in the central calorimeter region ({pipe}η{pipe}<0. 8) for jets with 60â€pT<800 GeV, and is maximally 14 % for pT<30 GeV in the most forward region 3. 2â€{pipe}η{pipe}<4. 5. The jet energy is validated for jet transverse momenta up to 1 TeV to the level of a few percent using several in situ techniques by comparing a well-known reference such as the recoiling photon pT, the sum of the transverse momenta of tracks associated to the jet, or a system of low-pT jets recoiling against a high-pT jet. More sophisticated jet calibration schemes are presented based on calorimeter cell energy density weighting or hadronic properties of jets, aiming for an improved jet energy resolution and a reduced flavour dependence of the jet response. The systematic uncertainty of the jet energy determined from a combination of in situ techniques is consistent with the one derived from single hadron response measurements over a wide kinematic range. The nominal corrections and uncertainties are derived for isolated jets in an inclusive sample of high-pT jets. Special cases such as event topologies with close-by jets, or selections of samples with an enhanced content of jets originating from light quarks, heavy quarks or gluons are also discussed and the corresponding uncertainties are determined. © 2013 CERN for the benefit of the ATLAS collaboration
Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector
The inclusive and dijet production cross-sections have been measured for jets
containing b-hadrons (b-jets) in proton-proton collisions at a centre-of-mass
energy of sqrt(s) = 7 TeV, using the ATLAS detector at the LHC. The
measurements use data corresponding to an integrated luminosity of 34 pb^-1.
The b-jets are identified using either a lifetime-based method, where secondary
decay vertices of b-hadrons in jets are reconstructed using information from
the tracking detectors, or a muon-based method where the presence of a muon is
used to identify semileptonic decays of b-hadrons inside jets. The inclusive
b-jet cross-section is measured as a function of transverse momentum in the
range 20 < pT < 400 GeV and rapidity in the range |y| < 2.1. The bbbar-dijet
cross-section is measured as a function of the dijet invariant mass in the
range 110 < m_jj < 760 GeV, the azimuthal angle difference between the two jets
and the angular variable chi in two dijet mass regions. The results are
compared with next-to-leading-order QCD predictions. Good agreement is observed
between the measured cross-sections and the predictions obtained using POWHEG +
Pythia. MC@NLO + Herwig shows good agreement with the measured bbbar-dijet
cross-section. However, it does not reproduce the measured inclusive
cross-section well, particularly for central b-jets with large transverse
momenta.Comment: 10 pages plus author list (21 pages total), 8 figures, 1 table, final
version published in European Physical Journal
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